In the assistant driver's or passenger's air bag system of this kind, an air bag and an inflater are attached to a holding member (e.g., a container), and a module cover is further attached to cover the air bag. At the collision of a vehicle, the inflater operates so that the air bag expands. The module cover is opened into the compartment as it is pushed by the expanding air bag until the air bag largely expands in the compartment to protect the assistant driver.
This module cover is formed with a tear starting line (or tear line) or a bend starting line so that it is pushed by the air bag, when the inflater operates. Then, the module cover is torn or bent along that starting line until it is opened into the compartment.
The assistant driver's air bag system of this kind has to be firmly fixed to the vehicle and to constitute a container which will not be deformed by the gas pressure of the inflater. Thus, the container is frequently made of a thick metal. To the container, moreover, there is fixed the inflater having a heavy weight before the assembly of the air bag. As a result, the weight of the container is so high that heavy works are required for assembling the air bag system (especially for fitting the folded air bag in the container). Specifically, the folded air bag is snugly accommodated in the container while changing the direction of the container many times. This requires manual works for handling the heavy container. Thus, a high man power is required for charging the air bag to thereby raise problems that the working fatigue is serious and that the assembling efficiency is low.